Microsoft on the hunt for 'serious' Windows flaw

Microsoft bug squashers are investigating reports of a serious security vulnerability in Windows operating systems that could allow attackers to take control of vast numbers of machines, particularly those located off US shores.

A Microsoft spokesman had only minimal details about the investigation, which was prompted by a presentation last week by researcher Beau Butler at the Kiwicon security conference in New Zealand. According to this report in the Sydney Morning Herald, the flaw affects every version of Windows including Vista and is actually the continuation of an old vulnerability that Microsoft supposedly fixed years ago.

The bug, according to Symantec's DeepSight threat notification service, resides in a feature known as Web Proxy Autodiscovery (WPAD), which helps IT administrators automate the configuration of proxy settings in Internet Explorer and other web browsers. The vulnerability can be "widely exploited" to "intercept web sessions, direct browsers to malicious proxies, and effectively gain control over unsuspecting users' web traffic," according to Symantec, which said it had yet to confirm the vulnerability.

Vulnerable browsers will traverse a company's host domain to search for a WPAD data file used to set up the proxy feature. IE running on host a.b.c.d.net, for example, first would look in b.c.d.net, then c.d.net and finally d.net. "In certain configurations, the third-level domain is not a trusted part of the network; an attacker can set up a malicious driftnet-type WPAD server situated outside of an organization's normal administrative control," Symantec warned.

"Now that we understand the issue we're researching comprehensive mitigations and workarounds to protect customers," Microsoft's general manager of product security, George Stathakopoulos, wrote in an email to the Sydney Morning Herald. Engineers in Australia and the US were scrambling to replicate and confirm the issue over the US Thanksgiving holiday, according to the paper. A Microsoft spokesman had no additional details on Monday.

Microsoft appears to have released a patch for the vulnerability in 1999. But the patch only protected domain names ending in .com, so WPAD servers using all other addresses have remained vulnerable. ®